Not just in the future—the impact is already significant, a new study argues.

Almost every major storm is now accompanied by a climate change discussion. Everybody wants to ask whether human impacts on the climate system “caused” the storm. Unless framed carefully, it’s kind of a lousy question. We can’t say for sure that an individual storm wouldn’t have occurred if we hadn’t warmed the planet by roughly 1°C—climate is, by definition, statistical. So we use analogies like the climate loading the dice (or juicing its hits like a steroid-assisted major leaguer). What we do know is that every storm now takes place in a world that's notably warmer than it was a century ago.

Perhaps no type of storm draws as much attention in the US as hurricanes, but the science of these storms has been dissatisfyingly uncertain. Some studies have projected more hurricanes in the future, but others have projected fewer. The best information available today points to decreasing frequency but increasing strength, but it comes with significant uncertainties.

One challenge is that global climate models used to make projections for the future have a hard time effectively simulating the fine-scale processes within hurricanes, which has contributed to the present uncertainty. Modern hurricane observations are also much better than they were in the past, so it’s difficult to identify historical trends in any of these details.

A new study published in the Proceedings of the National Academy of Sciences tries to get around this limitation by examining a different kind of hurricane record—storm surge records from six tide gauges along the southeast coast of the US, which extend back to 1923. By building probability distributions, they were able to look at changes in extremes as well as averages. The researchers also removed the effect of sea level rise to separate the magnitude of the storms from the climbing baseline caused by rising oceans.

The resulting data was compared to possible contributing factors, such as the El Niño Southern Oscillation, average global temperature, local temperature around the Earth, and sea surface temperature in the tropical Atlantic. Since hurricanes are fueled by warm surface water, the data correlated most strongly with global temperature and sea surface temperatures in the area where hurricanes form.

The researchers used these relationships to create statistical models of hurricane behavior. Based on the last 90 years, those models calculated that a 1°C warming of the globe increases the probability of a hurricane storm surge the size of Hurricane Katrina’s by two to seven times—a startling rise.

That’s larger than previous estimates, which relied on climate model simulations. If accurate, the study tells us that putting hurricanes on climate steroids will have costly consequences. But it also tells us that the warming of the 20th century is already affecting us in a significant way. The paper concludes that “we have probably crossed the threshold where Katrina magnitude hurricane surges are more likely caused by global warming than not.” In other words, storm surges of that size are now at least twice as common as they were a century ago.

Put sea level rise back in the equation, and each surge becomes a little more destructive. For the city of New Orleans, which was devastated by Katrina, the reality is even uglier—bigger hurricane surges on top of rising sea level and a sinking city.

Add a few feet to your hits in baseball, and balls that used to land short of the outfield wall start to count as home runs. Add enough warming to your climate system, and some storm surges that used to stop short of flooding may start to count as disasters.

100 Reader Comments

I've been wondering if my region will start to see bigger and more powerful storms. I'm on the northern coast of California, and the climate is remarkably mild here. It's been a few years since we've taken any damage from a strong Pacific storm.

I've been reading some of the financial information about the government flood insurance - mostly that it is in the red with the past few major storms, but they expect to get out of that hole in a few years. At least, with the expectation that these last few major storms are rare events.

I dearly hope that I misunderstand and that they are really planning for this kind of flooding to be the new normal. I certainly expect it to be.

I've been wondering if my region will start to see bigger and more powerful storms. I'm on the northern coast of California, and the climate is remarkably mild here. It's been a few years since we've taken any damage from a strong Pacific storm.

This makes sense, given my limited knowledge of hurricane formation, which can basically be summed up as: warm water causes hurricanes. Still, hurricanes always make me think of Niven's "Lucifer's Hammer" in which the hurricanes that result from the meteor impact do far more damage than the initial impact. Scary stuff.

If you add to the amount of free energy in a chaotic system (which certainly describes weather) you're going to see more extremes. The whole point is that climate change increases the variation of our weather, not that it's going to make temps go up or down.

If you add to the amount of free energy in a chaotic system (which certainly describes weather) you're going to see more extremes. The whole point is that climate change increases the variation of our weather, not that it's going to make temps go up or down.

Shush, you fanatic! How DARE you bring science and logic into this conversation?!

Scary thought, but we'll need to formulate a theory on how increased global mean temperatures could actually impact human ignorance and do a study to see if there's a correlation between changes in average temperatures and changes in human ignorance.

US hurricanes have been in a lull for a while, so it would be reasonable to suspect that the number of land falling hurricanes will increase in the near future. I have not read the paper so I will not criticize the results, but they are making two big assumptions, first that temperature increases since the 1920's have increased hurricane surge levels and two that the temperature will go up 1 degree in the near future.

I thought most of the flooding damage to NOLA was due to the failure of the levees holding back Lake Ponchartrain, not storm surge (although storm surge may be what caused the levees to fail). Is that not correct?

I've been wondering if my region will start to see bigger and more powerful storms. I'm on the northern coast of California, and the climate is remarkably mild here. It's been a few years since we've taken any damage from a strong Pacific storm.

Hurricane Sandy was the last extreme surge we've had here in the US and that was the result of a few variables lining up just right not the warming of the globe. What many call a perfect storm. Katrina was government's failure to provide proper levies. I can't think of any other examples of extreme surges in the US in recent history. Anyone one else?

Scary thought, but we'll need to formulate a theory on how increased global mean temperatures could actually impact human ignorance and do a study to see if there's a correlation between changes in average temperatures and changes in human ignorance.

Psst... We have experts called climatologists and meteorologists doing this. You make it sound like no one is watching...

I am curious about how they take into account the differences between a storm making landfall with the tide coming in (high or real high tide) and the tide going out since that will greatly effect the amount of storm surge a storm generates even if they are of they same intensity and strength.

Also I wonder if they took into account erosion and storm surge since the amount of construction on the coasts of many areas hit has greatly eroded due to massive population explosions in the past 30 years or so. If the coastlines are shallower due to excessive sand erosion storm surge can intensify greatly due to sand erosion more so than the rise of temperature by 0.1 degree.

But they do state in the article that they actually lack any certainty in accuracy so I guess we are back to conjecture and guessing in yet another study.

I would hope for some more science leaning towards the actual accuracy of the data rather than a presentation that appears more to push a political/corporate agenda. Skewed presentations aren't science. They are marketing.

US hurricanes have been in a lull for a while, so it would be reasonable to suspect that the number of land falling hurricanes will increase in the near future. I have not read the paper so I will not criticize the results, but they are making two big assumptions, first that temperature increases since the 1920's have increased hurricane surge levels and two that the temperature will go up 1 degree in the near future.

Actually I think if you read the article again you'll see that the paper actually CALCULATES that surge levels have increased, and they are talking about the 1C temperature rise (actually around 0.8C globally) that has already happened. Its a correlation study, they're not proving causal links here, but OTOH it doesn't take a lot of imagination to come up with cause -> effect. Note they correlated a bunch of different variables.

There are of course some possible statistical pitfalls with this kind of analysis. If you cast your net wide enough you will eventually find some sort of correlations (either in time or in terms of different variables). There are of course well-known ways to control for that. I think overall I'll accept that chances are their statistics are OK, its not a hard thing to get right, and see if any reviewers criticize that. It would be nice to be able to review the statistics on every paper, but sure would be impossible to do.

I am curious about how they take into account the differences between a storm making landfall with the tide coming in (high or real high tide) and the tide going out since that will greatly effect the amount of storm surge a storm generates even if they are of they same intensity and strength.

Also I wonder if they took into account erosion and storm surge since the amount of construction on the coasts of many areas hit has greatly eroded due to massive population explosions in the past 30 years or so. If the coastlines are shallower due to excessive sand erosion storm surge can intensify greatly due to sand erosion more so than the rise of temperature by 0.1 degree.

But they do state in the article that they actually lack any certainty in accuracy so I guess we are back to conjecture and guessing in yet another study.

I would hope for some more science leaning towards the actual accuracy of the data rather than a presentation that appears more to push a political/corporate agenda. Skewed presentations aren't science. They are marketing.

Calls to mind all that politically based fear mongering that followed Sandy. All the claims that global warming was the cause of Sandy even when experts were saying this was not the case and were providing the actual fact and science behind why Sandy was so devastating.

Hurricane Sandy was the last extreme surge we've had here in the US and that was the result of a few variables lining up just right not the warming of the globe. Katrina was government's failure to provide proper levies. I can't think of any other examples of extreme surges in the US in recent history. Anyone one else?

Ike, Andrew and more before they started naming them, seems like it's the 100 year storm every decade. Katrina was also both government screw up and an extreme surge.

Hurricane Sandy was the last extreme surge we've had here in the US and that was the result of a few variables lining up just right not the warming of the globe. Katrina was government's failure to provide proper levies. I can't think of any other examples of extreme surges in the US in recent history. Anyone one else?

Ike, Andrew and more before they started naming them, seems like it's the 100 year storm every decade. Katrina was also both government screw up and an extreme surge.

Ike and Andrew were not extreme storms. Nor were they 100 year storms.

Hurricane Sandy was the last extreme surge we've had here in the US and that was the result of a few variables lining up just right not the warming of the globe. Katrina was government's failure to provide proper levies. I can't think of any other examples of extreme surges in the US in recent history. Anyone one else?

Ike, Andrew and more before they started naming them, seems like it's the 100 year storm every decade. Katrina was also both government screw up and an extreme surge.

Ike and Andrew were not extreme storms. Nor were they 100 year storms.

Considering that 100 storms and extreme storms don't have a set of universally agreed properties, but are more of opinions, sure they were.

Investigating storm surge is an interesting concept, but it will be too easy to make correlations which do not really tie together sound evidence.

For example, Katrina was an extremely powerful storm when it hit land and had a massive 14ft storm surge across the region. Sandy was a fairly weak storm...but still managed to have a whopping 12.5 ft storm surge.

However, the reasons for Sandy's surge have nothing to do with storm intensity (which could be attributed to climate change through higher water temperatures) and everything to do with the massive SIZE of the storm. What exactly made Sandy so large is still being discussed and debated today.

I thought most of the flooding damage to NOLA was due to the failure of the levees holding back Lake Ponchartrain, not storm surge (although storm surge may be what caused the levees to fail). Is that not correct?

The levees failed in many places because the water overtopped them. In a few spots, that wasn't the case- I'm not sure if those failures would have occurred given a smaller surge.http://soundwaves.usgs.gov/2006/01/

US hurricanes have been in a lull for a while, so it would be reasonable to suspect that the number of land falling hurricanes will increase in the near future. I have not read the paper so I will not criticize the results, but they are making two big assumptions, first that temperature increases since the 1920's have increased hurricane surge levels and two that the temperature will go up 1 degree in the near future.

There are a few mixed up issues here. The number of storms in the North Atlantic Basin have been high (historically speaking) since the mid to late '90s. The number of US landfalling storms has no relation to the number or energy of the storms in a season. For example, in 2010, there were 19 named storms with 5 major hurricanes (cat. 3 and above), a very active season, third most active season, depending on ho you want to count. However, there were no hurricanes that made a US landfall in 2010. In 1992 there were 7 named storms and one major storm, Hurricane Andrew which came ashore as a cat. 5 hurricane, an extremely rare and devastating event. It only takes one.

I have not been able to read the paper yet but there are so may pieces to the hurricane puzzle that it is dangerous to pull one out without a very robust reason (statistical or not). The SST is a factor but really it is depth to the 26 deg. C isotherm that will tell you more about the potential for a hurricane to get lots of energy. Even if the top 2 meter are hot as hell it won't get you very far when it comes to hurricanes (exaggeration for effect). It is also not surprising that landfalling hurricanes with significant storm surge are correlated to regions SST in regions where hurricanes form. This can be seen in inter-annual variability. Color me underwhemled so far (I really should read the paper but ...).

I agree that humans are impacting the environment and that we need to do something now. But one observation makes me wonder about this. The biggest storms in our solar system are on Jupitor. But Jupitor is a very cold place. Actually, at the other extreme, the Sun seems to have some big storms. Who is to say that any one temperature is more natural than any other one? Again, we need to stop creating green house gasses, but we should still expect there will be climate change - just not caused by us.

Who's to say any one kind of planetary/solar storm is different than another?

I agree that humans are impacting the environment and that we need to do something now. But one observation makes me wonder about this. The biggest storms in our solar system are on Jupitor. But Jupitor is a very cold place. Actually, at the other extreme, the Sun seems to have some big storms. Who is to say that any one temperature is more natural than any other one? Again, we need to stop creating green house gasses, but we should still expect there will be climate change - just not caused by us.

Jupiter has no significant land features, and a very thick atmosphere (it's almost entirely atmosphere). There's nothing to get in the way of a storm system once it starts except another storm, and bigger ones can sustain themselves by sucking up or deflecting smaller ones. There's also a very large temperature gradient between the top and bottom of the planet's atmosphere; Jupiter actually puts out more energy by itself than it gets from the Sun. Just because it's cold doesn't mean it's not an energetic, dynamic system.

Investigating storm surge is an interesting concept, but it will be too easy to make correlations which do not really tie together sound evidence.

For example, Katrina was an extremely powerful storm when it hit land and had a massive 14ft storm surge across the region. Sandy was a fairly weak storm...but still managed to have a whopping 12.5 ft storm surge.

However, the reasons for Sandy's surge have nothing to do with storm intensity (which could be attributed to climate change through higher water temperatures) and everything to do with the massive SIZE of the storm. What exactly made Sandy so large is still being discussed and debated today.

Sandy can't be compared to Katrina. Sandy's surge was due to other factors what just happened to line up at the right time to magnify the storm. Katrina was bad thanks to poor levies.